Introduction
Autism spectrum disorder (ASD) is a developmental disorder that affects communication, social interaction, and behavior. The causes of ASD are not fully understood, but some environmental factors, such as exposure to valproic acid (VPA), a drug used to treat epilepsy and bipolar disorder, during pregnancy, have been linked to an increased risk of ASD in offspring.
One of the possible mechanisms by which VPA induces ASD is by impairing the function of Purkinje cells, a type of neuron in the cerebellum that is involved in motor coordination and cognitive processes. Purkinje cells are highly sensitive to iron overload, which can cause oxidative stress and cell death. VPA can increase iron levels in Purkinje cells by disrupting the process of ferritinophagy, which is the selective degradation of ferritin, a protein that stores and regulates iron, by autophagy, a cellular recycling system.
Ferritinophagy is mediated by two proteins: ULK1, which initiates autophagy, and NCOA4, which binds to ferritin and delivers it to the autophagosome, a membrane-bound structure that fuses with the lysosome, where ferritin is degraded and iron is released. VPA can inhibit ULK1 activity and reduce NCOA4 expression, resulting in impaired ferritinophagy and iron accumulation in Purkinje cells.
A recent study has discovered a natural compound that can protect Purkinje cells from VPA-induced ferritinophagy impairment and ASD-like features. The compound is called ligustilide, and it is derived from the root of celery, a common vegetable.
What is ligustilide and how does it work?
Ligustilide is a bioactive component of celery root that has anti-inflammatory, antioxidant, and neuroprotective properties. It has been used in traditional Chinese medicine for treating various disorders, such as stroke, dementia, and menstrual pain.
The researchers found that ligustilide can restore ferritinophagy in Purkinje cells by activating ULK1 and increasing NCOA4 expression. By doing so, ligustilide can reduce iron levels, oxidative stress, and cell death in Purkinje cells exposed to VPA. Moreover, ligustilide can also modulate the expression of genes related to ASD, such as BDNF, GABA, and glutamate, which are involved in neuronal development, synaptic plasticity, and neurotransmission.
How did the researchers test the effects of ligustilide?
The researchers used two experimental models to test the effects of ligustilide: a cell culture model and an animal model.
In the cell culture model, they treated rat Purkinje cells with VPA, ligustilide, or both, and measured the levels of ferritin, iron, NCOA4, ULK1, and markers of oxidative stress and cell viability. They found that VPA increased ferritin and iron levels, decreased NCOA4 and ULK1 levels, and induced oxidative stress and cell death in Purkinje cells. Ligustilide reversed these effects by restoring ferritinophagy and protecting Purkinje cells from VPA-induced damage.
In the animal model, they injected pregnant rats with VPA on the 12th day of gestation, and then treated the offspring with ligustilide or saline from the 21st to the 35th day after birth. They then performed behavioral tests and brain tissue analysis on the offspring. They found that VPA-exposed offspring exhibited ASD-like features, such as impaired social interaction, repetitive behavior, and cognitive deficits. Ligustilide improved these behavioral abnormalities and normalized the expression of ASD-related genes in the cerebellum of VPA-exposed offspring.
What are the implications and limitations of this study?
This study suggests that ligustilide, a natural compound from celery root, can protect Purkinje cells from VPA-induced ferritinophagy impairment and ASD-like features by activating ULK1 and increasing NCOA4 expression. This finding provides a novel insight into the molecular mechanism of ASD and a potential therapeutic strategy for preventing or treating ASD.
However, this study also has some limitations that need to be addressed in future research. First, the dose and duration of ligustilide treatment used in this study may not be optimal or applicable for human use. Second, the effects of ligustilide on other brain regions and cell types involved in ASD, such as the cortex and microglia, are not clear. Third, the safety and efficacy of ligustilide in humans, especially in pregnant women and children, have not been established. Therefore, more studies are needed to confirm the beneficial effects of ligustilide and to explore its potential clinical applications for ASD.
Faq
What is valproic acid (VPA) and how does it induce ASD-like features?
Valproic acid (VPA) is a medication that is used to treat epilepsy, bipolar disorder, and migraine. It works by stabilizing the electrical activity of the brain and preventing seizures or mood swings. However, VPA can also have side effects, such as causing birth defects or increasing the risk of autism spectrum disorder (ASD) in the offspring of pregnant women who take VPA.
One of the possible mechanisms by which VPA induces ASD-like features is by impairing the function of Purkinje cells, a type of neuron in the cerebellum that is involved in motor coordination and cognitive processes. Purkinje cells are highly sensitive to iron overload, which can cause oxidative stress and cell death. VPA can increase iron levels in Purkinje cells by disrupting the process of ferritinophagy, which is the selective degradation of ferritin, a protein that stores and regulates iron, by autophagy, a cellular recycling system.
What is ferritinophagy and why is it important for Purkinje cells?
Ferritinophagy is the process of breaking down ferritin, a protein that stores and regulates iron, by autophagy, a cellular recycling system. Ferritinophagy is important for Purkinje cells, a type of neuron in the cerebellum that is involved in motor coordination and cognitive processes, because it helps them maintain a healthy balance of iron. Iron is essential for Purkinje cells to function properly, but too much iron can cause oxidative stress and cell death.
How does iron accumulation affect Purkinje cells and ASD-like features?
Iron accumulation affects Purkinje cells and ASD-like features by inducing oxidative stress and cell death. Oxidative stress is a condition where there is an imbalance between the production of reactive oxygen species (ROS) and the ability of the cell to neutralize them. ROS can damage the DNA, proteins, and lipids of the cell, leading to cell dysfunction or death. Cell death can reduce the number and function of Purkinje cells, which can impair the cerebellar circuitry and affect the communication with other brain regions. This can result in ASD-like features, such as impaired social interaction, repetitive behavior, and cognitive deficits.
What are the behavioral tests used to assess the ASD-like features of the offspring of VPA-exposed rats?
The behavioral tests used to assess the ASD-like features of the offspring of VPA-exposed rats are:
- The three-chamber test, which is used to measure the social interaction and preference of the rats. The test involves placing the rat in a chamber with three compartments, one containing a novel object, one containing a novel rat, and one empty. The time spent in each compartment and the number of entries into each compartment are recorded and compared.
- The marble burying test, which is used to measure the repetitive and compulsive behavior of the rats. The test involves placing the rat in a cage with 20 marbles on the bedding, and observing the number of marbles buried by the rat within 15 min.
- The Morris water maze test, which is used to measure the spatial learning and memory of the rats. The test involves placing the rat in a circular pool filled with water, where a hidden platform is located in one of the four quadrants. The rat has to find the platform using visual cues around the pool. The latency to find the platform, the distance traveled, and the time spent in each quadrant are recorded and analyzed.
What are the advantages and disadvantages of using the rat model of VPA-induced ASD?
The rat model of VPA-induced ASD is an experimental model that involves the injection of VPA to pregnant rats on the 12th day of gestation, and then the observation and analysis of the offspring for ASD-like features. The rat model of VPA-induced ASD has some advantages and disadvantages, such as:
- Advantages:
- The rat model of VPA-induced ASD can mimic some of the neurodevelopmental and behavioral abnormalities of human ASD, such as impaired social interaction, repetitive behavior, and cognitive deficits, which can facilitate the study of the pathogenesis and treatment of ASD.
- The rat model of VPA-induced ASD can allow the manipulation and measurement of various molecular and cellular parameters, such as gene expression, epigenetic regulation, ferritinophagy, iron homeostasis, oxidative stress, and cell death, which can elucidate the mechanisms and factors involved in ASD.
- The rat model of VPA-induced ASD can enable the testing and evaluation of various interventions and therapies for ASD, such as ligustilide, which can provide evidence and insights for the prevention or treatment of ASD.
- Disadvantages:
- The rat model of VPA-induced ASD may not fully reflect the complexity and heterogeneity of human ASD, as ASD is a spectrum disorder that can vary in severity and symptoms from person to person, and can be influenced by various genetic and environmental factors, besides VPA exposure.
- The rat model of VPA-induced ASD may have some limitations and biases in the experimental design and execution, such as the dose and timing of VPA exposure, the genetic background and sex of the rats, the behavioral tests and brain tissue analysis methods, and the statistical analysis and interpretation of the results, which can affect the validity and reliability of the findings.
- The rat model of VPA-induced ASD may have some ethical and practical issues in the translation and application of the findings to humans, such as the animal welfare and rights, the safety and efficacy of the interventions and therapies, and the regulatory and clinical requirements and standards, which can pose challenges and barriers for the development and implementation of ASD interventions and therapies.
Source:
https://www.sciencedirect.com/science/article/abs/pii/S0944711324001089